Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 169-173).

Terahertz (THz) reflection and transmission spectroscopy is a promising new field with applications in imaging and illicit material detection. One particularly useful application is for the detection of improvised explosive devices (IEDs) which is a favorite weapon of global terrorists. Explosive materials have been shown to have a unique spectral signature in the THz band which can be used to identify the explosives. However, the initial measurements performed on the explosive samples do not account for the modulation of the spectral features by random scattering that will be prevalent with actual samples encountered in applications. The intent of this work is to characterize and quantify the effects of random scattering that may alter the spectral features. Specifically, the effect that a randomly rough surface and granular scattering has on the scattered THz wave (T-Rays) will be investigated and characterized using the Finite-Difference Time-Domain (FDTD) simulation method. The FDTD method is a natural choice for this work as it can handle complicated geometries (i.e., multiple scatterers, arbitrarily rough interfaces, etc.) arbitrary materials (i.e., dispersive media, etc.) and provides broadband frequency data with one simulation pass. First, the effect that the randomly rough surface of the sample explosive has on the extracted spectral signature will be studied using a Monte-Carlo analysis. Then the effect of the complex structure inside the explosive material (the granular scatterers) will be considered. Next, when the physics of the rough surface and granular scattering are understood, a robust method to extract the spectral signature from the reflected T-rays will be developed.

No description available.

A method for determining percent cloud cover by taking two consecutive images using different color contrast filters, specifically a red filter and a blue filter, is described. This method (RF/BF estimate) involves dividing the "red" image by the "blue" image, pixel by pixel, and determining the percentage of pixels in the resultant image with intensity values of one. This is the percent cloud cover. The RF/BF estimate is based on the different effects of molecule and particle scattering of electromagnetic waves in the visible portion of the spectrum. These two types of scattering, Rayleigh and Mie scattering respectively, are described as they relate to this methodology. The RF/BF estimates are compared to visual estimates of percent cloud cover using the northern portion of 100 Central Florida skies collected during the period from January 28, 1988 to February 25, 1988. A strong correlation r=0.94 was found between the RF/BF and visual estimates. Advantages of the method are discussed along with implications and suggestions for follow-up studies.

This thesis examines backscattering from prolate spheroids at microwave frequencies.

The series of experimental studies to be described has been carried out in order to determine the feasibility of using corner reflectors as laboratory standards for model cross-section measurements.

Thesis (PhD) -- Stellenbosch University, 1991. / ENGLISH ABSTRACT: This dissertation investigates the moment method solution of electromagnetic radiation and scattering problems using parallel computers. In particular, electromagnetically large problems with arbitrary geometries are considered. Such problems require a large number of unknowns to obtain adequate approximate solutions, and make great computational demands. This dissertation considers in detail the efficient exploitation of the potential offered by parallel computers for solving such problems, and in particular the class of local memory Multiple Instruction, Multiple Data systems. A brief history of parallel computing is presented. Methods for quantifying the efficiency of parallel algorithms are reviewed. The use of pseudo-code for documenting algorithms is discussed and a pseudo-code notation is defined that is used in later chapters. A new parallel conjugate gradient algorithm, suitable for the solution of general systems of linear equations with complex values, is presented. A method is described to handle efficiently the Hermitian transpose of the matrix required by the algorithm. Careful attention is paid to the theoretical analysis of the algorithm's parallel properties (in particular, speed-up and efficiency). Pseudo-code is presented for the algorithms. Timing results for a moment method code, running on a transputer array and using this conjugate gradient solver, are presented and compared to the theoretical predictions. A parallel LU algorithm is described and documented in pseudo-code. A new graphical description of the algorithm is presented that simplifies the identification of the parallelism and the analysis of the algorithm. The use of formal methods for extracting parallelism via the use of invariants is presented and new examples given. The speed-up and efficiency of the algorithm are analyzed theoretically, using new methods that are simpler than those described in the literature. Techniques for optimizing the efficiency of parallel algorithms are introduced, and illustrated with pseudo-code. New parallel forward and backward substitution algorithms using the data distribution required for the parallel LV algorithm are described, and documented with pseudo-code. Results obtained with a Occam 2 moment method code running on a transputer array using these parallel LU solver and substitution algorithms are presented and compared with the theoretical predictions. PARNEC, a new Occam 2 implementation of the thin-wire core of NEC2, is discussed. The basic 'theory of NEC2 is reviewed. Problems with early attempts at combining Occam and FORTRAN are reported. Methodologies for re-coding an old code written in an unstructured language in a. modern structured language are discussed. Methods of parallelizing the matrix generation are discussed. The accuracy of large moment method formulations is investigated, as is the effect of machine precision on the solutions. The use of the biconjugate gradient method to accelerate convergence is briefly considered and rejected. The increased size of problem that can be handled by PARNEC, running on a transputer array, is demonstrated. Conclusions are dra.wn regarding the contributions of this dissertation to the development of efficient parallel electromagnetic moment method algorithms. / AFRIKAANSE OPSOMMING: Hierdie proefskrif ondersoek die momentmetode oplossing van elektromagnetiese straling- en strooiingprobleme d.m.v. multiverwerkers. In besonder, elektromagneties groot probleme met arbitrere geometriee word beskou. Sulke probleme vereis 'n groot aantal onbekendes om 'n voldoende benaderde oplossing te kry, en stel groot berekenings vereistes. Hierdie proefskrif beskou in detail die doeltreffende benutting van die potensiaal wat multiverwerkers vir sulke problem hied, in besonder die klas van lokale geheue Veelvoudige Instruksie, Veelvoudige Data stelsels. 'n Kort geskiedenis van multiverwerkers word gegee. Metodes vir die kwantifisering van die effektiwiteit van multiverwerkers word hersien. Die . gebruik van pseudokode vir die dokumentering van algoritmes word bespreek en 'n pseudokode notasie word gedefinieer wat gebruik word in latere hoofstukke. 'n Nuwe parallelle toegevoegde helling-algoritme wat geskik is vir die oplossing van algemene stelsels van lineere vergelykings word aangebied. 'n Metode word beskryf om op 'n doeltreffende wyse die Hermitiese transponent van die matriks, wat deur die algoritme benodig word, te hanteer. Sorgvuldige aandag word aan die teoretiese analise van die paralleleienskappe van die algoritme gegee (in die besonder, versnelling en doeltreffendheid). Pseudokode word aangebied vir die algoritmes. Resultate vir die looptyd van 'n momentmetode program, wat op 'n transputerskikking loop, word gegee en vergelyk met die teoretiese voorspellings. 'n Parallelle L U algoritme word beskryf en gedokumenteer in pseudokode. 'n Nuwe grafiese beskrywing van die algoritme, wat die identifikasie van parallelisme en die analise van die algoritme vergemaklik, word gegee. Die gebruik van formele metodes vir die onttrekking van parallelisme d.m.v. invariante word getoon en nuwe voorbeelde word gegee. Die versnelling en doeltreffendheid van die algoritme word teoreties geanaliseer, d.m.v. nuwe metodes wat eenvoudiger is as die wat in die literatuur beskryf word. Tegnieke vir die optimering van die doeltreffendheid van parallelle algoritmes word ingevoer, en gelllustreer met pseudokode. Nuwe parallelle voor- en truwaarts-substitusie algoritmes wat die data verspreiding van die parallelle LU algoritme gebruik word beskryf, en gedokumenteer met pseudokode. Resultate verkry met 'n Occam 2 momentmetode program wat op 'n transputerskikking loop en die parallelle L U en substit'usie algoritmes gebruik, word gegee en vergelyk met teoretiese voorspellings. PARNEC, 'n nuwe Occam 2 implementering van die dun-draad kern van NEC2, word bespreek. Die basiese teorie van NEC2 word opgesom. Verslag word gedoen oor probleme met vroee pogings orh Occam en FORTRAN te kombineer. Metodes om 'n ou program, geskryf in 'n ongestruktureerde taal, in 'n moderne gestruktureerde taal te herskryf word bespreek. Metodes om die matriksopwekking te paralleliseer word bespreek. Die akkuraatheid van groot momentmetode formulerings word ondersoek, asook die effek van masjienpresisie op die oplossings. Die gebruik van die dubbeltoegevoegde helling-metode om konvergensie te versnel word kortliks beskou en verwerp. Die vergrote probleemgrootte, wat met PARNEC op- 'n transputerskikking uitgevoer kan word, word gedemonstreer. Gevolgtrekkings word gemaak rakende die bydraes van hierdie proefskrif tot die ontwikkeling van doeltreffende parallelle elektromagnetiese momentmetode algoritmes.

The present research is a targeted endeavor to study the underlying characteristics and novel applications of millimeter (mm) wave through terahertz (THz) spectrum of electromagnetic (EM) energy. Focused thereof are the following specific tasks broadly considered pertinent to the said EM spectral range: (i) To elucidate the material characteristics vis-à-vis the interaction with EM energy at the test frequencies; (ii) to identify biomedical applications based on the material characteristics studied and applied to biomedia; and (iii) to model the wireless communication channels supporting EM waves at the test frequency bands of interest. Commensurate with the scope as above, the objectives of the research are as follows: / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

The modulated scattering technique is used in conjunction with a Software Defined Radio (SDR) dongle to obtain a software-based modulated signal output. SDR# is the software package used to get spectrum analysis of the modulated signal. A transmitter yagi antenna sends a 2.304GHz signal on to an antenna connected to a reflector coefficient modulator (700Hz) and the modulated waves are received by another yagi. The receiver yagi antenna is then connected to a frequency converter to convert a 2.304GHz signal to a 144MHz dongle input signal which finally puts the scattered output on computer software with a SDR dongle. The output has a center frequency with modulated spectral lines on either side of the measured frequency. Finally, antenna patterns are measured with different types of antennas by rotating the antennas and observing the baseband modulation sidebands.

Numerical analysis of the electromagnetic fields in large, complex structures is very challenging due to the high computational overhead. Recently, it has been shown that a new method called Trefftz-FLAME ( Flexible Local Approximation MEthod) is suitable for problems where there exist a large number of similar structures. / This thesis develops Trefftz-FLAME in two areas. First, a novel 2D Trefftz-FLAME method incorporates the modal analysis and port boundary condition that are essential to an accurate calculation of reflection and transmission coefficients for photonic crystal devices. The new technique outperforms existing methods in both accuracy and computational cost. / The second area pertains to the 3D, vector problem of electromagnetic wave scattering by aggregates of identical dielectric particles. A methodology for the development of local basis functions is introduced, applicable to particles of any shape and composition. Boundary conditions on the surface of the finite FLAME domain are described, capable of representing the incident wave and absorbing the outgoing radiation. A series of problems involving dielectric spheres is solved to validate the new method. Comparison with exact solutions is possible in some cases and shows that the method is able to produce accurate near-field results even when the computational grid spacing is equal to the radius of the spheres.